Abstract
This paper proposes an enhanced control strategy for mitigating state-transition oscillations in active and reactive power responses of self-synchronized converter system to secure the islanded power system stability. The self-synchronized converter is well known for “grid-forming” that is able to operate to stand-alone mode (SAM) providing grid voltage and frequency without phase synchronization units. Although the grid-forming (GFM) is self-synchronized, the inherent synchronization principle causes system degradation in which should maintain a point of common coupling (PCC) voltage for critical loads as well as transitions from grid-connected mode (GCM) to SAM and vice versa. Therefore, this paper focuses on resolving the inherent oscillatory issues in GFM self-synchronized converter system (especially adopted ‘synchronverter’ principle), and proposes a control strategy for controllability improvement based on stability analysis for smooth state-transition under islanded power system. The efficacy of the proposed control method is verified through a high-fidelity electromagnetic transient (EMT) simulation with case studies on 30kW synchronverter system and further experimental hardware-in-loop system (HILS) test with Opal-RT (OP-5707) platform.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Synchronverter proposed in the initial paper has been developed as an enabler to operate with other electrical machines in securing the power system stability, and it is assumed that a generation resource and constant PQ load through an aggregation are included in the system topology without certain complicated network and multiple converters
The AC grid and converter system are modeled in Op-5707 of Opal-RT simulator [33], and modeled synchronverter is controlled by external DSP hardware board (TMS320F28377) [34]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The previous research could improve the self-synchronized system stability and control flexibility, that research is not considered with several important conditions as follows: 2 It should be accounted for under an islanding condition with critical loads requiring a necessary grid service to provide the high quality power generated from RESs, the previous research concentrate only on the large grid interconnection condition with other SMs. IIDRs-based generation system should be capable of maintaining and recovering an islanded grid voltage and frequency with SAM operation, GCM operation as well as mode transition. This paper focuses on controllability improvement of the synchronverter system without any modification of the inherent synchronous machine features, and investigates SAM to GCM transition condition with critical loads change in islanded power system that is not considered in previous studies.
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